Among the power amplifying method for use in amplification or the like of transmission signals in communication devices, according to the LINC (Linear Amplification with Nonlinear Component) method, an input signal having envelope variation is converted into two constant envelope signals having a phase difference in accordance with the amplitude of the input signal, and the resultant constant envelope signals are amplified using non-linear amplifiers. Thereafter, the amplified constant envelope signals are vector-added to each other to thereby obtain an amplified input signal. According to this method, as the non-linear amplifier amplifies just constant envelope signals, it is possible to improve power amplification efficiency (see, e.g., Patent Document 1).    Patent Document 1: JP Publication No. Hei 6-22302